Diaphragm valves selectively operable to restrict or permit fluid flow are generally well known in the art. Such valves conventionally include a weir or valve seat. An elastomeric or plastic diaphragm can be set against and removed from the valve seat responsively to rotation of a valve stem. The valve stem serves to transfer forces which in turn deflect the diaphragm and hence open and close the valve. A handwheel is typically rotatably coupled to the valve stem for exerting rotational forces to the valve stem sufficient to deflect the diaphragm. It is also well known manually actuated valves provided with elastomeric or plastic diaphragms may experience damage to the diaphragm during closing. During closing, the diaphragm may be exposed to high closing forces, ultimately resulting in premature failure and leakage through the valve.
One approach to solving this problem includes using a nut which acts as a travel stop and which is threaded on top of the valve stem. This nut is positioned on the valve stem such that it bears against the top of the valve bonnet when the valve stem has reached the intended limit during the closing. This travel stop protects the diaphragm from excessive forces during valve closing. This nut may be tapped in a flat to accommodate a set screw to secure the nut to the valve stem flat preventing movement of the nut. This nut can also serve as the drive mechanism between the valve stem and the handwheel. A shortcoming of this approach lies in the difficulty of adjusting the position of such a valve stop. In order to adjust the valve stop, typically one must completely remove a screw securing the handwheel to the valve stem, remove the handwheel, loosen the set screw, back the travel stop nut off the valve stem, rotate the valve stem to close the valve, rotate the travel stop nut to contact the bonnet thus setting the new travel stop, tighten the set screw to prevent inadvertent movement of the travel stop nut, reinstall the handwheel and resecure the handwheel to the valve stem. This typically requires a technician using at least three separate tools at great time and expense.
U.S. Pat. No. 5,377,956 ('956 patent), entitled "DIAPHRAGM VALVE" issued Jan. 3, 1995, the entire disclosure of which is hereby incorporated by reference as if being set forth in its entirety herein. The '956 patent describes the use of a limiter screw nut threadably enagaged with an exterior of a valve stem and which bears upon an upper body of the valve for limiting the closing lift of the valve stem. As is well known though, there are a number of reasons which may prevent the valve from fully closing, and such a configuration undesirably requires fully removing the handwheel and cap to fully close the valve in such an instance. Further, complete removal of the handwheel and cap are also required to access the limiter screw nut in order to change its position relative to the valve stem and hence change the closing travel stop of the valve.
Accordingly, it is an object of the present invention to overcome these shortcomings, and provide a diaphragm valve that facilitates easier repositioning of the valve stop.
It is a further object of the present invention to provide a diaphragm valve which does not require the handwheel to be completely removed in order to adjust the valve stop for the valve stem.